JP2015035535A - Group iii nitride semiconductor epitaxial substrate, and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a group III nitride semiconductor epitaxial substrate which enables the achievement of both of excellent surface flatness and the reduction in warp.SOLUTION: A group III nitride semiconductor epitaxial substrate 10 according to the present invention comprises: a substrate 12 with at least a surface portion made of AlN; an undoped AlN layer 14; an AlN buffer layer 16; and a superlattice laminate 20 in turn. The AlN buffer layer 16 is doped with Si at an impurity concentration larger than 1.0×10/cm. The superlattice laminate 20 is arranged by laminating a high-Al-containing layer 21A, and further laminating n combinations each consisting of a low-Al-containing layer and a high-Al-containing layer; the low-Al-containing layer and the high-Al-containing layer are stacked alternately (provided that n is an integer which meets the condition: 4≤n≤10). From the side of the AlN buffer layer 16, the first to (n-2)th low-Al-containing layers 21B have a first thickness, the (n-1)th low-Al-containing layer 22B has a second thickness larger than the first thickness. The n-th low-Al-containing layer 23B has a third thickness equal to or larger than the second thickness.

Description

  The present invention relates to a group III nitride semiconductor epitaxial substrate and a method for manufacturing the same. In particular, the present invention relates to a group III nitride semiconductor epitaxial substrate capable of achieving both excellent surface flatness and reduced warpage, and a method for manufacturing the same.

  In recent years, group III nitride semiconductors composed of compounds of Al, Ga, In, and the like and N have been widely used in light emitting elements, electronic device elements, and the like. Since the characteristics of such a device are greatly influenced by the surface flatness at the atomic level of the group III nitride semiconductor, a technique for growing a group III nitride semiconductor excellent in surface flatness is required.

  The group III nitride semiconductor is formed by epitaxial growth on a substrate made of sapphire, SiC, Si or GaAs. However, the group III nitride semiconductors and these substrates have greatly different lattice constants and thermal expansion coefficients. Therefore, when a group III nitride semiconductor is grown on these substrates, the strain of the group III nitride semiconductor formed on the substrate becomes large due to various reasons such as lattice mismatch and difference in thermal expansion coefficient. Therefore, it was difficult to obtain excellent surface flatness at the atomic level. Therefore, after forming an AlN buffer layer on the substrate, a superlattice laminate in which AlN layers and AlGaN layers are alternately epitaxially grown is formed on the buffer layer, whereby surface flatness is formed on the superlattice laminate. It is known that an excellent group III nitride layer can be grown. This is because stress can be relaxed and dislocations can be reduced by the superlattice laminate while eliminating the mismatch between the thermal expansion coefficient and the lattice constant by the AlN buffer layer.

  Here, in Patent Document 1, an AlN buffer layer is formed on a Si substrate, a composition gradient layer in which the composition is inclined on the AlN buffer layer so that the Al composition decreases in the crystal growth direction, and a high Al content layer Disclosed is a group III nitride semiconductor epitaxial substrate formed by sequentially forming superlattice composite layers in which low Al-containing layers are alternately stacked. Moreover, according to the technique described in Patent Document 1, it is possible to obtain a group III nitride semiconductor layer having high crystallinity by forming a group III nitride semiconductor layer on the group III nitride semiconductor epitaxial substrate. It is.

JP 2009-158804 A

  In order to obtain a group III nitride semiconductor epitaxial substrate excellent in surface flatness using the superlattice laminate described in Patent Document 1, two high Al content layers and low Al content layers are alternately used as the superlattice laminate. Even if only one layer is laminated, the effect of suppressing the generation of pits on the surface of the group III nitride semiconductor epitaxial substrate is recognized. However, according to a more detailed study by the present inventors, in order to most effectively suppress the generation of pits, a considerable number of alternating layers (for example, 40 layers of high Al content layers and low Al content layers alternately) Above) It was found that it was necessary to laminate. As the number of superlattice stacks increases, the dislocations that propagate by relaxing the stress inside the crystal can be reduced. As a result, a group III nitride semiconductor epitaxial substrate having excellent surface flatness can be obtained. Can be obtained. However, when the number of superlattice laminates increases, the warpage of the group III nitride semiconductor epitaxial substrate increases due to the difference in thermal expansion coefficient between the superlattice laminate and the substrate. Therefore, realization of excellent surface flatness and realization of reduced warpage are in a trade-off relationship. Here, the warp of the group III nitride semiconductor epitaxial substrate is a group III nitride formed by further forming a layer functioning as a semiconductor element (hereinafter simply referred to as “element formation layer”) on the group III nitride semiconductor epitaxial substrate. For a physical semiconductor element, it can cause cracks, and can also be a hindrance when processing into a device. Accordingly, there is a need for a group III nitride semiconductor epitaxial substrate that has both excellent surface flatness and reduced warpage, and a method for manufacturing the same. The “crack” means a crack or crack that does not divide the substrate.

  In view of the above problems, an object of the present invention is to provide a group III nitride semiconductor epitaxial substrate that has both excellent surface flatness and reduced warpage, and a method for manufacturing the same.

In order to achieve the above object, the gist of the present invention is as follows.
(1) A substrate having at least a surface portion made of AlN, an undoped AlN layer formed on the substrate, an AlN buffer layer formed on the undoped AlN layer, and a superlattice formed on the AlN buffer layer In a group III nitride semiconductor epitaxial substrate having a laminate,
The AlN buffer layer is Si-doped with an impurity concentration greater than 1.0 × 10 ¹⁹ / cm ³ , and the superlattice stack has an average composition x in the crystal growth direction of 0.9 <on the AlN buffer layer. A high Al content layer (Al _x Ga _1-x N) consisting of x ≦ 1 is laminated, and a low Al content layer (Al _y Ga _1-y N) where the average composition y in the crystal growth direction is 0 <y <x. ) And the high Al-containing layer are alternately stacked in n groups (where n is an integer satisfying 4 ≦ n ≦ 10), and the first (n−2) counting from the AlN buffer layer side. The first low Al-containing layer has a first thickness, and the (n-1) th low Al-containing layer has a second thickness that is greater than the first thickness, and the nth Wherein the low Al-containing layer has a third thickness not less than the second thickness. Group nitride semiconductor epitaxial substrate.

(2) The group III nitride semiconductor epitaxial substrate according to (1), wherein the low Al-containing layer is a composition gradient layer in which an Al composition decreases along a crystal growth direction.

(3) The group III nitride semiconductor epitaxial substrate according to (1) or (2), wherein the high Al content layer satisfies 0.95 ≦ x ≦ 1.

(4) The group III nitride semiconductor epitaxial substrate according to (3), wherein the high Al content layer is an AlN layer (x = 1).

(5) The group III nitride semiconductor epitaxial substrate according to any one of (1) to (4), wherein the third thickness is thicker than the second thickness.

(6) The group III nitride semiconductor epitaxial substrate according to any one of (1) to (5), wherein the high Al content layer has an equal thickness.

(7) A step of forming an undoped AlN layer on a substrate having at least a surface portion made of AlN, a step of forming an AlN buffer layer on the undoped AlN layer, and a superlattice laminate on the AlN buffer layer In a method for producing a group III nitride semiconductor epitaxial substrate having a step,
In the step of forming the AlN buffer layer, Si is doped so as to have an impurity concentration greater than 1.0 × 10 ¹⁹ / cm ^3, and in the step of forming the superlattice laminate, a crystal is formed on the AlN buffer layer. A high Al content layer (Al _x Ga _1-x N) having an average composition x in the growth direction of 0.9 <x ≦ 1 is stacked, and an average composition y in the crystal growth direction is a low value of 0 <y <x. In stacking n sets of Al-containing layers (Al _y Ga _1-y N) and the high Al-containing layers alternately (where n is an integer satisfying 4 ≦ n ≦ 10),
The thickness of the low Al-containing layer from the first to the (n-2) th counting from the AlN buffer layer side is the first thickness, and the thickness of the (n-1) th low Al-containing layer is A Group III nitride semiconductor epitaxial substrate characterized in that the second thickness is greater than the first thickness, and the thickness of the nth low Al-containing layer is a third thickness equal to or greater than the second thickness. Manufacturing method.

  ADVANTAGE OF THE INVENTION According to this invention, the group III nitride semiconductor epitaxial substrate which enabled the coexistence of the outstanding surface flatness and the reduced curvature, and its manufacturing method can be provided.

1 is a schematic cross-sectional view of a group III nitride semiconductor epitaxial substrate 10 according to an embodiment of the present invention. FIG. 3 is an enlarged view of a first stacked body 21 in the group III nitride semiconductor epitaxial substrate 10 of FIG. 1. It is a surface photograph of the group III nitride semiconductor epitaxial substrate concerning the comparative example 5 (trial example 10). It is a TEM cross-sectional photograph of the group III nitride semiconductor epitaxial substrate concerning the comparative example 5 (trial example 10). It is a surface photograph of the group III nitride semiconductor epitaxial substrate concerning the comparative example 3 (trial example 8). It is a surface photograph of the group III nitride semiconductor epitaxial substrate concerning Example 1 (trial example 1). It is a TEM cross-sectional photograph of the group III nitride semiconductor epitaxial substrate concerning Example 1 (trial example 1). 1 is an example of a group III nitride semiconductor light emitting device 50 formed by providing an element constituent layer 30 on a group III nitride semiconductor epitaxial substrate 10 according to an embodiment of the present invention. It is a figure which shows an example of the time-dependent change of the mixing ratio of TMG (trimethylgallium) and TMA (trimethylaluminum) in the manufacturing method of the group III nitride semiconductor epitaxial substrate 10 of this invention. It is a figure which shows an example of the time-dependent change of the mixing ratio of TMG and TMA in the manufacturing method of the group III nitride semiconductor epitaxial substrate 10 of this invention. It is a schematic cross section of the substrate for explaining the definition of the warpage amount (SORI). It is a TEM cross-sectional photograph of the group III nitride semiconductor epitaxial substrate concerning Example 1 (trial example 1), Comprising: It is an enlarged photograph of the superlattice laminated body part.

  Hereinafter, an embodiment of a group III nitride semiconductor epitaxial substrate of the present invention will be described with reference to the drawings. 1, 2, and 8, for convenience of explanation, the thickness of each layer is exaggerated with respect to the substrate, unlike the actual thickness ratio. 1 and 8, a part of the laminated structure of the superlattice laminate 20 is omitted. In addition, in the present specification, when simply expressed as “AlGaN”, the chemical composition ratio of the group III element (total of Al and Ga) and N is 1: 1, and the ratio of the group III element Al and Ga is It shall mean any indefinite compound. The expression “AlGaN” does not exclude AlN. Further, when the ratio of the Al composition in the group III element in this compound does not change in the crystal growth direction, it is particularly referred to as “Al content”. Note that the AlN layer and the surface portion in the present invention are both single crystal AlN layers, and are not AlN layers mainly composed of polycrystal or amorphous grown at a low temperature of 900 ° C. or lower, for example.

As shown in FIG. 1, a group III nitride semiconductor epitaxial substrate 10 according to an embodiment of the present invention includes a substrate 12 having at least a surface portion made of AlN, an undoped AlN layer 14 formed on the substrate 12, An AlN buffer layer 16 formed on the undoped AlN layer 14 and a superlattice laminate 20 formed on the AlN buffer layer 16 are included. As will be described in detail later, the superlattice laminate 20 is a high Al content layer (Al _x Ga _1-x N) on the AlN buffer layer 16 where the average composition x in the crystal growth direction is 0.9 <x ≦ 1. Further, n sets of low Al-containing layers (Al _y Ga _1-y N) and high Al-containing layers having an average composition y in the crystal growth direction of 0 <y <x are alternately arranged (where n is 4). (It is an integer satisfying ≦ n ≦ 10). Here, the first to (n−2) th low Al content layers counted from the AlN buffer layer side have the first thickness, and the (n−1) th low Al content layer is the first. The n-th low Al-containing layer has a third thickness that is equal to or greater than the second thickness.

  Here, in the superlattice laminate 20, a laminate composed of layers from the high Al content layer immediately above the AlN buffer layer 16 to the (n−2) th high Al content layer counted from the AlN buffer layer 16 side is referred to as “ This is referred to as “first laminated body 21”. The high Al content layer in the first laminate 21 is represented as a high Al content layer 21A, and the low Al content layer is represented as a low Al content layer 21B. Further, the low Al-containing layer immediately above the first laminate 21 is represented as a low Al-containing layer 22B, and the high Al-containing layer on the low Al-containing layer 22B is represented as a high Al-containing layer 22A. A laminate including the Al-containing layer 22A is referred to as a “second laminate 22”. Further, the low Al content layer immediately above the second laminate 22 is represented as a low Al content layer 23B, and the high Al content layer on the low Al content layer 23B is represented as a high Al content layer 23A. A laminate including the Al-containing layer 23A is referred to as a “third laminate 23”. That is, the low Al content layer 22B is the (n−1) th low Al content layer counted from the AlN buffer layer side and has the second thickness. The low Al content layer 23B is the nth low Al content layer counted from the AlN buffer layer side and has a third thickness.

As the substrate 12 having at least a surface portion made of AlN, an AlN template substrate in which an AlN single crystal is formed on a substrate made of a metal such as sapphire, SiC, Si, diamond, or Al, and an AlN in which the entire substrate is AlN. And a single crystal substrate. The thickness of the substrate 12 is appropriately set in consideration of the warpage amount after epitaxial growth of each layer, and is in the range of, for example, 400 to 2000 μm. The AlN on the surface portion of the substrate 12 used in the present invention has good crystallinity. For example, the half width of the AlN on the (102) plane by X-ray rocking curve diffraction (XRC) is 600 seconds or less. It is preferable that it is a substrate. The dislocation density is preferably 1.0 × 10 ⁹ / cm ² or less. This is because the use of a substrate with few dislocations can suppress the risk of cracks due to excessive dislocations when using a Si-doped AlN buffer layer 16 described later.

An undoped AlN layer 14 is formed on the substrate 12. The undoped AlN layer 14 is intended to take over the AlN crystallinity of the substrate 12 with good crystallinity, and has a thickness in the range of 10 to 50 nm. The term “undoped” here means that impurities are not intentionally doped, and does not intend to exclude unavoidable impurities due to the device or diffusion. Specifically, the impurity concentration of impurities that can be p-type or n-type which are not inevitable impurities in undoping can be defined as 5.0 × 10 ¹⁶ / cm ³ or less. This is a concentration that does not contribute to electrical conduction in a light emitting device such as an LED.

On the undoped AlN layer 14, an AlN buffer layer 16 having an AlN composition and Si-doped with an impurity concentration greater than 1.0 × 10 ¹⁹ / cm ³ is formed. In this specification, the impurity concentration means a value obtained by converting the peak value of the detected intensity of the impurity obtained by SIMS (Secondary Ion-microprobe Mass Spectrometer) into a concentration. The reason why the AlN buffer layer 16 is Si-doped so as to have an impurity concentration greater than 1.0 × 10 ¹⁹ / cm ³ will be described later.

Hereinafter, the details of the superlattice laminate 20 will be described with reference to FIGS. 1 and 2.
On the AlN buffer layer 16, the superlattice laminate 20 composed of the first laminate 21, the second laminate 22, and the third laminate 23 is formed. As described above, the superlattice laminate 20 includes a high Al content layer (Al _x Ga _1-x N) having an average composition x in the crystal growth direction of 0.9 <x ≦ 1, and an average in the crystal growth direction. Two types of AlGaN layers having an average Al composition are alternately laminated with low Al-containing layers (Al _y Ga _1-y N) having a composition y of 0 <y <x. Here, regarding the average composition x of Al in the high Al content layer, “Al _x Ga _1-x N (0.9 <x ≦ 1)” means that the Al composition is constant in the high Al content layer. Even if it exists, it may change continuously or discontinuously, and it means that the Al average composition x in the crystal growth direction is 0.9 <x ≦ 1. It is the same meaning that the Al average composition y of the low Al-containing layer is represented as “Al _y Ga _1-y N (0 <y <x ≦ 1)”. Further, the high Al content layers 21A to 23A have the same Al average composition x. Similarly, the low Al content layers 21B to 23B have the same Al average composition y.

  In addition, regarding the number of superlattice stacks 20, the number of stacks of the low Al content layer and the high Al content layer that are alternately formed excluding the high Al content layer on the AlN buffer layer 16 is set to n (where n Is an integer satisfying 4 ≦ n ≦ 10). When n is used, the first stacked body 21 has one high Al-containing layer 21A stacked on the AlN buffer layer 16, and the low Al-containing layer 21B and the high Al-containing layer 21A are alternately arranged in this order (n− 2) It is formed by stacking a set. The film thickness of the high Al-containing layer 21A can be about 1 to 10 nm. Each high Al content layer 21A in the 1st laminated body 21 can take arbitrary values within this range, respectively. On the other hand, the first thickness, which is the thickness of the low Al-containing layer 21B, can be about 0.5 to 1.5 nm, but the first thickness is constant in the first stacked body 21. The total film thickness of the first stacked body 21 can be about 3 to 92 nm.

  In the second stacked body 22 on the first stacked body 21, a low Al-containing layer 22B having a second thickness larger than the first thickness and a high Al-containing layer 22A are stacked one by one in this order. The film thickness of the high Al-containing layer 22A can be about 1 to 10 nm, and may be the same as or different from the film thickness of the high Al-containing layer 21A of the first stacked body 21. On the other hand, the film thickness (second thickness) of the low Al-containing layer 22B is 1.5 to 2 under the condition that the film thickness is thicker than the first thickness of the low Al-containing layer 21B of the first stacked body 21. About 5 nm. The total film thickness of the second stacked body 22 can be about 2.5 to 12.5 nm.

  On the 2nd laminated body 22, the 3rd laminated body 23 formed by laminating | stacking the low Al content layer 23B which has 3rd thickness more than 2nd, and the high Al content layer 23A one by one in this order. Is formed. The film thickness of the high Al-containing layer 23A can be about 1 to 10 nm, and the film thickness of the high Al-containing layer 21A of the first stacked body 21 and / or the same film as the high Al-containing layer 22A of the second stacked body. The thickness may be different or different. On the other hand, under the condition that the film thickness (third thickness) of the low Al-containing layer 23B is equal to or greater than the film thickness (second thickness) of the low Al-containing layer 22B of the second stacked body 22, 1.5 to It can be about 3.5 nm. In other words, in the film thickness of the low Al-containing layer, the second thickness described above is thicker than the first thickness. And although 2nd thickness and 3rd thickness may be the same thickness, it is more preferable that 3rd thickness becomes thicker than 2nd thickness so that it may mention later. Regarding the low Al-containing layer, the layers whose thicknesses may be changed are one layer of the low Al-containing layer 22B having the second thickness and one layer of the low Al-containing layer 23B having the third thickness. The thickness of three layers or more of the low Al content layer cannot be continuously changed. This is because the state in which only nucleation on the same surface described below remains is lost, and the effects of the present invention are not achieved. As can be seen from this, the design philosophy is greatly different between the known superlattice structure performed to relieve stress and the superlattice structure of the present invention.

  Here, the upper limit of the number n of pairs in which the low Al-containing layer and the high Al-containing layer are alternately stacked is set to 10, because the defect occurrence positions are aligned by reducing the total thickness, and the defects are This is to promote the planarization of the group III nitride semiconductor epitaxial substrate 10 as a result. The number n of alternately stacked layers is preferably 5 or more and 7 or less (5 ≦ n ≦ 7), and most preferably 6 (n = 6). Details of the reason why this number of alternately stacked layers is suitable will be described later together with the reason why the AlN buffer layer 16 is doped with Si at a predetermined concentration. However, stress can be relieved by setting n to 5 or more. The defect can be further reduced by setting n to 7 or less. Further, by setting n to 6, these effects can be obtained most. Note that the superlattice laminate 20 is formed by alternately stacking, for example, six sets (n = 6) of low Al-containing layers and high Al-containing layers after the high Al-containing layer 21A formed on the AlN buffer layer 16. When this is done, it is said that the number of stacks of superlattice stack 20 is “6.5 sets”. That is, if the above-described n is used, the number of stacked groups of the superlattice stacked body 20 can be expressed as (n + 0.5) groups.

  The group III nitride semiconductor epitaxial substrate 10 according to the embodiment of the present invention is characterized by an AlN buffer layer 14 doped with Si at a predetermined concentration as described above, and a superlattice laminate 20 formed on the AlN buffer layer 14. It is. By adopting such a configuration, the present invention has a remarkable effect that the group III nitride semiconductor epitaxial substrate 10 capable of achieving both excellent surface flatness and reduced warpage can be obtained.

The technical significance of adopting such a configuration will be described below including the effects.
In order to reduce warpage, the present inventors have studied various surface flatnesses when the number of superlattice laminates 20 formed on the AlN buffer layer 16 is reduced. The impurity concentration for doping Si into the AlN buffer layer 16 is 1.0 × 10 ¹⁹ / cm ³ or less, the number of superlattice laminates 20 is 40.5, and the second and third laminates A group III nitride semiconductor epitaxial substrate according to trial example 10 (details will be described later in the examples) were formed. At this time, irregularities of random height were formed on the surface of the n-type contact layer formed on the superlattice laminate 20 as shown in the surface photograph shown in FIG. From the cross-sectional view of the group III nitride semiconductor epitaxial substrate according to Trial Example 10 obtained using the TEM shown in FIG. 4, this unevenness is due to a plane defect originating from the vicinity of the outermost surface of the superlattice laminate 20. I understand. It is expected that the unevenness of the random height is due to the random generation origin position in the vertical direction of the surface defect.

  On the other hand, 6.5 sets in which the number of stacks of the superlattice stack 20 is significantly reduced from 40.5 while further providing the second and third stacks without changing the impurity concentration of Si doping. In the group III nitride semiconductor epitaxial substrate according to trial example 8 (details will be described later in the examples), the n-type formed on the superlattice laminate 20 as shown in the surface photograph of FIG. The surface of the contact layer was uneven, but the height of the convex surface was uniform. This is considered to be because the generation of the surface defects in the vertical direction is the same plane due to the further provision of the second and third laminates, and only those that have not disappeared are left. In addition, if there was no 2nd and 3rd laminated body, the height of the convex surface was not uniform.

Further, according to the present invention, the second and third laminated bodies are provided in the superlattice laminated body 20 so that the number of laminated groups is 6.5, and the impurity concentration for Si doping is more than 1.0 × 10 ¹⁹ / cm ^3. When the group III nitride semiconductor epitaxial substrate is used, the surface of the n-type contact layer formed on the superlattice laminate 20 is not uneven as shown in the surface photograph of FIG. It was all right. A TEM cross-sectional view at this time is shown in FIG. Note that the surface photograph of FIG. 6 and the TEM cross-sectional photograph of FIG. 7 were obtained using the group III nitride semiconductor epitaxial substrate according to Trial Example 1, and details will be described later in the examples. From FIG. 7, in the state where the origin of surface defects in the vertical direction is the same surface, the amount of surface defects is increased and saturated by increasing the amount of Si doping, and as a result, the same surface is generated and generated. The present inventors consider that this is because almost all adjacent surface defects are merged and disappeared when the surface defects are elongated in the growth direction.

  Here, since the Si doping to the AlN buffer layer 16 has the effect of forming irregularities on the surface of the AlN buffer layer 16 and roughening the surface, in order to obtain a semiconductor epitaxial substrate having excellent surface flatness, It was avoided. However, as described above, the present inventors have noted that by providing the second and third stacked bodies, only the uneven surface having the same height is formed on the top surface of the superlattice stacked body 20. . The inventors of the present invention improve the flatness of the uppermost surface of the superlattice laminate 20 by doping the AlN buffer layer 16 with a large amount of Si to increase and saturate the convex surfaces having the same height. I found. Further, at the same time as improving the flatness, the AlN buffer layer 16 is doped with a large amount of Si, so that many defects are introduced into the AlN buffer layer 16 and stress is reduced. As a result, warping is reduced. It is done. As described above, the flatness of the uppermost surface of the superlattice laminate 20 is uniform as described above when only the first laminate is formed as the superlattice laminate 20, and the dislocations are random. As a result, only the dislocations in a certain direction are left by the formation of the second laminate and the third laminate, which are different from the first laminate in the thickness of the low Al content layer, and the strain is reduced by the formation of the surface defect. The present inventors believe that this is because of this. Then, by the above-described action of the second and third laminates, the number of superlattice laminates is compared with the number of conventionally known superlattice laminates required to suppress the generation of pits. Thus, it was possible to reduce the number to 10.5 or less (that is, the maximum value of n was 10).

Thus, in order to achieve both high surface flatness at the atomic level and reduced warpage, the inventors have made the AlN buffer layer 16 Si-doped at an impurity concentration higher than 1.0 × 10 ¹⁹ / cm ^3. In addition, the present inventors have found that the object of the present invention can be achieved by providing the superlattice laminate 20 including the low Al-containing layers 21B to 23B having the first, second, and third thicknesses, respectively. It came to complete.

  Although the present invention is not limited by theory, the group III nitride semiconductor epitaxial substrate 10 of the present embodiment can achieve both high surface flatness at the atomic level and reduced warpage due to the above-described action. It is thought that there is a remarkable effect.

  As will be described later in Examples, when the superlattice laminate 20 composed of the first laminate 21 and the second laminate 22 is formed without forming the third laminate 23, excellent surface flatness Moreover, it was impossible to achieve both the reduced warpage. From this, it is essential that the superlattice laminate 20 includes both the second laminate 22 and the third laminate 23 as in the present embodiment. This is presumably because dislocation cannot be made only in a certain direction by only one low Al-containing layer having a thickness greater than the first thickness of the low Al-containing layer 21B.

  Here, in the present embodiment, the third thickness of the low Al-containing layer 23B is more preferably thicker than the second thickness of the low Al-containing layer 22B. By generating a stress different from that of the second stacked body, the direction of dislocation can be changed, the dislocation annihilation action can be more expected, and the group III nitride semiconductor epitaxial substrate 10 with more excellent surface flatness can be obtained. .

  In addition, the high Al content layers 21A to 23A are preferable because they have the same thickness, so that a stress relaxation effect can be further obtained.

In one embodiment, the low Al-containing layers 21B to 23B made of Al _y Ga _1-y N where the average composition in the crystal growth direction is 0 <y <x include the composition gradient that decreases the Al composition along the crystal growth direction. A layer is preferred. A layer having an Al composition constant in the crystal growth direction with respect to the composition gradient layer is referred to as a “composition rectangular layer”. Even if the low Al content layer 21B-23B is any of a composition inclination layer and a composition rectangular layer, the effect of this invention is acquired. However, for the following reasons, it is more preferable that the low Al-containing layers 21B to 23B are composition gradient layers.

  As described above, the composition gradient layer is a layer whose composition is inclined so that the Al composition in AlGaN decreases continuously or discontinuously in the crystal growth direction. By tilting the Al composition of the composition gradient layer so as to decrease in the crystal growth direction, the thermal expansion coefficient of the low Al-containing layer becomes a relatively high Al composition on the surface of the composition gradient layer on the substrate 12 side, and the expansion coefficient of the substrate. Get closer to. On the other hand, the surface of the composition gradient layer on the crystal growth direction side has a relatively low Al composition and approaches the thermal expansion coefficient of the element formation layer when the element formation layer is formed on the group III nitride semiconductor epitaxial substrate 10, It can be expected that the occurrence of cracks can be further suppressed.

  As the composition of the composition gradient layer, when the value of the Al composition in AlGaN is y1 on the side close to the substrate 12 and y2 on the surface in the crystal growth direction, preferably 0.7 ≦ y1 ≦ on the side close to the substrate 12. It is the range of x, More preferably, it is the range of 0.9 <= y1 <= x. Further, the surface on the crystal growth direction side is preferably in the range of 0 ≦ y2 <0.3, and more preferably in the range of 0 ≦ y2 <0.1. If the Al composition is within the above range and the composition is tilted from y1 to y2 in the crystal growth direction, the difference in lattice constant between the substrate 12 and the composition gradient layer can be reduced. As a result, the crystallinity when the element forming layer is formed Can be improved.

Note that the Al composition of Al _y Ga _1-y N in the composition gradient layer may be continuous or discontinuous as long as it decreases in the crystal growth direction. Further, the rate at which the Al composition decreases in the crystal growth direction may be constant or irregular. When the composition is continuously changed from y1 to y2 at a constant rate in the crystal growth direction, it can be expressed as an average composition y = (y1 + y2) / 2.

  The high Al-containing layer may be either a composition gradient layer or a composition rectangular layer, but a composition rectangular layer in which the Al composition is constant in the crystal growth direction is preferred.

  The Al average composition x of the high Al-containing layers 21A to 23A is preferably 0.95 ≦ x ≦ 1. This is because the difference in Al average composition between the adjacent low Al-containing layers is increased and the strain buffering effect is improved. However, it is more preferable that the high Al content layers 21A to 23A are all AlN layers (that is, x = 1). This is because the difference in Al average composition between adjacent low Al-containing layers is maximized and the strain buffering effect is maximized.

As described above, the effect of the present invention can be obtained if the impurity concentration of doping Si into the AlN buffer layer 14 is higher than 1 × 10 ¹⁹ / cm ³ . Here, if it is 2 × 10 ¹⁹ / cm ³ or more, the effect of the present invention can be obtained more reliably, which is preferable. However, the impurity concentration is more preferably less than 8 × 10 ¹⁹ / cm ³ . This is because at 8 × 10 ¹⁹ / cm ³ or more, the dislocation caused by the AlN buffer layer becomes excessive and cracks may occur.

  The group III nitride semiconductor epitaxial substrate 10 according to the present invention can be used for any semiconductor element such as a light emitting element, a laser diode, and a transistor. FIG. 8 shows a semiconductor light emitting device 50 formed using a group III nitride semiconductor epitaxial substrate 10 according to the present invention. For example, by epitaxial growth using a known method such as MOCVD, a connection layer 31, an n-type contact layer 32, an n-type cladding layer 33, and a multiple quantum well layer (on the superlattice laminate 20 ( An element formation layer 30 including an MQW layer) 34, a p-type cladding layer 35, and a p-type contact layer 36 is sequentially formed. After the formation of the element forming layer 30, a part of the n-type contact layer 32 is exposed by, for example, dry etching, and the n-side electrode 41 and the p-type contact layer 36 are formed on the exposed n-type contact layer 32 and p-type contact layer 36. By arranging the p-side electrode 42, the group III nitride light emitting device 50 having a lateral structure can be formed. In addition, after forming a bonding layer on the p-type contact layer and bonding it to another support substrate, a light emitting element having a vertical structure can be formed after removing the substrate by using a laser or a chemical lift-off method. .

  In the present specification, “AlGaN” constituting the high Al content layer and the low Al content layer may contain B and / or In which are other group III elements in total of 1% or less. Further, for example, a trace amount of impurities such as Si, H, O, C, Mg, As, and P may be contained, and Mg impurities may be partially added intentionally. In addition, AlN constituting the group III nitride laminate may similarly contain other group III elements in total of 1% or less.

  In the present specification, expressions such as “constant”, “equal”, “same”, “identical” do not mean equality in a strictly mathematical sense, but are inevitable errors in the manufacturing process. As a matter of course, it includes an error that is allowed within a range in which the operational effects of the present invention are exhibited, and this point is the same in other embodiments. As such an error, 3% or less is included in “constant”, “equal”, “same”, “same”.

(Method for producing Group III nitride semiconductor epitaxial substrate)
The method of manufacturing a group III nitride semiconductor epitaxial substrate 10 of the present invention includes a step of forming an undoped AlN layer 14 on a substrate 12 having at least a surface portion made of AlN, and an AlN buffer layer 16 formed on the undoped AlN layer 14. And a step of forming a superlattice laminate 20 on the AlN buffer layer 16. Here, in the step of forming the AlN buffer layer 16, Si is doped so as to have an impurity concentration higher than 1.0 × 10 ¹⁹ / cm ³ . Further, in the step of forming the superlattice laminate 20, a high Al content layer (Al _x Ga _1-x N) having an average composition x in the crystal growth direction of 0.9 <x ≦ 1 is laminated, and further crystal growth is performed. N sets of low Al-containing layers (Al _y Ga _1-y N) having an average composition y in the direction of 0 <y <x and the high Al-containing layers alternately (where n satisfies 4 ≦ n ≦ 10) In stacking (which is an integer), the thickness of the low Al-containing layer from the first to the (n−2) th from the AlN buffer layer 16 side is defined as the first thickness, and the (n−1) th low The thickness of the Al-containing layer is a second thickness that is greater than the first thickness, and the thickness of the nth low Al-containing layer is a third thickness that is equal to or greater than the second thickness. To do.

  As an epitaxial growth method of each layer in the present invention, known methods such as MOCVD method and MBE method can be used. Examples of source gases for forming AlGaN include TMA (trimethylaluminum), TMG (trimethylgallium), and ammonia. The Al composition in the film is controlled by adjusting the mixing ratio of TMA and TMG for each layer. This can be done by controlling according to the stage.

  That is, when the Al composition is constant as a composition rectangular layer in each layer, the Al composition is changed by changing the mixing ratio of TMA and TMG according to the growth stage of each layer as shown in FIG. Can be controlled. Moreover, if the epitaxial growth time is controlled, the film thickness of each layer can be arbitrarily controlled.

  Also in the case of forming a composition gradient layer, the composition gradient layer can be formed by changing the mixing ratio of TMG and TMA over time according to the epitaxial growth time of each layer. An embodiment in which an AlN layer is formed as a high Al content layer and the Al composition is gradually reduced gradually from 1 to 0.02 in the crystal growth direction will be described with reference to FIG.

  First, an AlN layer (a high Al content layer) is formed with the TMA ratio being 100% without flowing TMG gas. After that, without changing the TMA gas flow rate, the TMG gas starts to flow, and the TMG gas flow rate is changed from 0 sccm to the TMG flow rate at which the Al composition is theoretically 0.02 (Ga composition is 0.98) for a certain period of time. By continuously increasing the flow rate in between, an AlGaN composition gradient layer (low Al-containing layer) in which the Al composition is continuously reduced from 1 to 0.02 in the crystal growth direction is formed (the average composition of Al is 0). .51). Here, “theoretically, the TMG flow rate at which the Al composition becomes 0.02” means that a predetermined Al composition is obtained by flowing a predetermined TMA flow rate and a TMG flow rate under the crystal growth conditions of the apparatus to be used. Is the flow rate experimentally confirmed in advance. At this time, a layer having a sufficient thickness that enables quantitative analysis of the Al composition by SIMS may be formed, and the TMA flow rate and the TMG flow rate may be confirmed. In forming the composition gradient layer, the TMA gas flow rate is not necessarily constant, and may be changed according to the target Al composition. By repeating this, a stacked body (5 AlN layers and 4 AlGaN composition gradient layers) in which high Al-containing layers and low Al-containing layers are alternately stacked is formed as the first stacked body 21. Here, the thicknesses (first thicknesses) of the low Al-containing layers are all equal if the epitaxial growth time is equal. Next, an AlGaN composition gradient layer and an AlN layer as the second stacked body 22 are formed. By reducing the rate of increase in the TMG flow rate per hour compared to the case of the first laminate and increasing the rate of increase in the TMG flow rate per hour correspondingly, the Al composition is reduced to 0.02. Then, an AlGaN composition gradient layer (low Al content layer) thicker than the first stacked body is formed. Thereafter, the TMG flow rate is set to 0, and an AlN layer (high Al content layer) is formed. For example, in the formation of the second stacked body 22, when the epitaxial growth time while increasing the TMG flow rate is twice that of the first stacked body, the thickness of the low Al-containing layer 22B in the second stacked body 22 (second (Thickness) is twice the film thickness (first thickness) of the low Al-containing layer 21 </ b> B in the first stacked body 21. Further, as the third laminate 23, the rate of increase in the TMG flow rate per hour is further reduced as compared with the case of the second laminate, and the Al composition is increased while increasing the rate of increase in the TMG flow rate per hour correspondingly. Is reduced to 0.02, thereby forming an AlGaN composition gradient layer (low Al-containing layer) thicker than the second stacked body. Thereafter, the TMG flow rate is set to 0, and an AlN layer (high Al content layer) is formed. For example, when the epitaxial growth time while increasing the TMG flow rate in the third stacked body 23 is three times that of the first stacked body 21, the film thickness (third thickness) of the low Al-containing layer 23 B in the third stacked body 23. ) Is three times the film thickness (first thickness) of the low Al-containing layer 21 </ b> B in the first stacked body 21. In forming the composition rectangular layer and the composition gradient layer described with reference to FIGS. 9 and 10, the V / III ratio of ammonia to TMA and TMG may be determined as appropriate.

  For the evaluation of the Al composition and film thickness after epitaxial growth, known methods such as optical reflectance method, TEM-EDS, and photoluminescence can be used. For the film thickness of several nanometers to several tens of nanometers of the superlattice structure, values based on TEM measurement results are used. TEM and SIMS analysis were requested from EAG (Evans Analytical Group).

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail using an Example, this invention is not limited to a following example at all.

(Trial example 1)
An AlN template substrate in which an undoped single crystal AlN layer (thickness: 600 nm, half width of AlN (102) plane by X-ray Rocking Curve: 242 seconds) is formed on a sapphire substrate (thickness: 430 μm) Prepared. After forming an undoped AlN layer having a thickness of 21.6 nm on this AlN template substrate by flowing TMA: 11.5 sccm and NH ₃ : 575 sccm at a pressure of 10 kPa and a temperature of 1150 ° C. using the MOCVD method, TMA: A Si-doped AlN buffer layer having a thickness of 5.4 nm doped with Si having an impurity concentration of 2.0 × 10 ¹⁹ / cm ³ was formed by flowing 11.5 sccm, NH ₃ : 575 sccm, and SiH ₄ : 50 sccm. That is, an undoped AlN layer and a Si-doped AlN buffer layer are formed on the AlN template substrate. Next, the first stacked body, the second stacked body, and the third stacked body constituting the superlattice stacked body were sequentially epitaxially grown on the Si-doped AlN buffer layer.

In the first laminate, an AlN layer (average composition x = 1) having a constant composition with a film thickness of 8 nm was used as the high Al-containing layer (Al _x Ga _1-x N). In forming this high Al content layer (Al _x Ga _1-x N), TMA: 11.5 sccm and NH ₃ : 575 sccm were flowed for 300 seconds. Further, a composition gradient layer having a film thickness of 1 nm and an average composition y = 0.51 was used as the low Al-containing layer (Al _y Ga _1-y N). This in forming the low Al-containing layer _{(Al y Ga 1-y N} ), TMA: 11.5sccm, NH 3: while flowing 575Sccm, the flow rate of TMG during the 10-second epitaxial growth time constant from 0sccm to 45sccm Increased in proportion. The low Al content layer is theoretically considered to have an Al composition continuously decreasing from 1 to 0.02 along the crystal growth direction. In the first stacked body, a high Al-containing layer was formed on the AlN buffer layer, and thereafter, four sets of low Al-containing layers and high Al-containing layers were alternately stacked. The first high Al-containing layer is counted as 0.5 pairs and becomes 4.5 pairs. In forming the second laminate following the first laminate, the flow rate of TMG is the same as that of the first laminate except that the TMG flow rate is increased at a constant rate from 0 sccm to 45 sccm during the epitaxial growth time of 20 seconds. A containing layer (film thickness 2 nm, composition gradient layer having an average composition y = 0.51) and a high Al content layer (film thickness 8 nm, average composition x = 1) were sequentially formed. Further, as a third laminated body following the second laminated body, a low Al content is obtained in the same manner as in the first laminated body except that the flow rate of TMG is increased at a constant rate from 0 sccm to 45 sccm during an epitaxial growth time of 30 seconds. A containing layer (film thickness 3 nm, composition gradient layer having an average composition y = 0.51) and a high Al content layer (film thickness 8 nm, average composition x = 1) were sequentially formed. That is, in this trial example, the first laminate is 4.5 sets, the second laminate is 1 set, the third laminate is 1 set, and the number of superlattice laminates is 6.5 sets in total. n = 6.

  Thereafter, on the superlattice laminate, an undoped AlGaN layer (Al content: 0.7, thickness: 2400 nm) as a connection layer and an AlGaN layer (Al content: 0.6, as an n-type contact layer) A group III nitride semiconductor epitaxial substrate according to Example 1 was fabricated by sequentially epitaxially growing a thickness of 1200 nm.

In addition, as a growth method of each of the above layers, an MOCVD method using TMA (trimethylaluminum), TMG (trimethylgallium), and ammonia as raw materials was used. Nitrogen / hydrogen was used as the carrier gas. SiH ₄ (monosilane) was used for Si doping. The growth conditions for each layer were a pressure of 10 kPa and a temperature of 1150 ° C. Moreover, the Al composition ratio for each layer was controlled by controlling the supply ratio of TMA and TMG as described above with reference to FIGS.

(Trial example 2)
A Group III nitride semiconductor epitaxial substrate according to Example 2 was produced in the same manner as in Example 1 except that the impurity concentration due to Si doping into the AlN buffer layer was changed to 1.20 × 10 ¹⁹ / cm ³ . .

(Trial example 3)
A Group III nitride semiconductor epitaxial substrate according to Example 3 was produced in the same manner as in Example 1 except that the impurity concentration due to Si doping to the AlN buffer layer was changed to 4.00 × 10 ¹⁹ / cm ³ . .

(Trial example 4)
A Group III nitride semiconductor epitaxial substrate according to Comparative Example 1 was produced in the same manner as in Trial Example 1, except that the impurity concentration due to Si doping to the AlN buffer layer was changed to 4.00 × 10 ¹⁸ / cm ³ . .

(Trial example 5)
Except for changing the film thickness of the low Al-containing layer of the third laminate to 2 nm (that is, corresponding to the case where the second thickness and the third thickness are equal), The group III nitride semiconductor epitaxial substrate concerning No. 4 was produced.

(Trial example 6)
In forming a low Al-containing layer, the flow rate of TMG at each epitaxial growth time was fixed at 45 sccm, and a composition rectangular layer of Al _0.02 Ga _0.98 N (Al content: 0.02) was formed Produced a Group III nitride semiconductor epitaxial substrate according to Example 5 by the same method as in Trial Example 1.

(Trial example 7)
A Group III nitride semiconductor epitaxial substrate according to Comparative Example 2 was produced in the same manner as in Trial Example 3 except that the third stacked body was not formed.

(Trial example 8)
Further, the second stacked body was not formed, and Comparative Example 3 was applied in the same manner as Trial Example 7 except that the impurity concentration by Si doping to the AlN buffer layer was changed to 4.00 × 10 ¹⁸ / cm ³ . A group III nitride semiconductor epitaxial substrate was fabricated.

(Trial example 9)
Group III nitriding according to Comparative Example 4 was performed in the same manner as in Example 1 except that the number of stacks in the first stack was 40.5, and the second and third stacks were not formed. A physical semiconductor epitaxial substrate was produced.

(Trial example 10)
A Group III nitride semiconductor epitaxial substrate according to Comparative Example 5 was produced in the same manner as in Trial Example 9 except that the impurity concentration due to Si doping to the AlN buffer layer was changed to 4.00 × 10 ¹⁸ / cm ³ . .

  The substrate formation conditions of the group III nitride semiconductor epitaxial substrates according to the above trial examples 1 to 10 are collectively shown in Table 1.

(Evaluation 1: Surface flatness)
About the group III nitride semiconductor epitaxial substrate of each trial example, the metal microscope apparatus (made by Nikon) was used, the surface photograph of the n-type contact layer surface was acquired, and the presence or absence of surface unevenness | corrugation was determined. If there is no surface irregularity, it means that the surface flatness of the group III nitride semiconductor epitaxial substrate is excellent. The results are shown in Table 1. In Table 1, those having surface irregularities were evaluated as x, and those having no surface irregularities were evaluated as ◯. 4 to 6 are surface photographs of a group III nitride semiconductor epitaxial substrate according to Trial Example 10 (Comparative Example 5), Trial Example 8 (Comparative Example 3), and Trial Example 1 (Example 1), respectively. This is shown here as a representative example.

  Furthermore, the TEM cross-sectional photograph of the group III nitride semiconductor epitaxial substrate was acquired about the group III nitride semiconductor epitaxial substrate of each trial example, and the surface defect was evaluated. The results are shown in Table 1. In Table 1, those having surface defects were evaluated as x, and those having no surface defects were evaluated as ◯. FIGS. 7 and 4 described above are TEM cross-sectional photographs of a group III nitride semiconductor epitaxial substrate according to Example 1 (Example 1) and Example 10 (Comparative Example 5), respectively. This is shown here as a representative example of the presence or absence of surface defects on the substrate. When surface defects of the group III nitride semiconductor epitaxial substrate according to the trial examples 1 to 3, 5, and 6 (that is, the examples 1 to 5) were observed, as in FIG. When the defects extend in the growth direction, it is considered that almost all adjacent surface defects are merged and disappeared, and no surface defects were observed. On the other hand, when the surface defects of the group III nitride semiconductor epitaxial substrate according to trial examples 4 and 7 to 11 (that is, comparative examples 1 to 6) were observed, the origin was in the vicinity of the outermost surface of the superlattice laminate as in FIG. A surface defect was observed. In obtaining a TEM cross-sectional photograph, for trial example 1, an n-type AlGaN layer (Al content: 0.61, film thickness: 600 nm, dopant: Si) as an n-type cladding layer, activity Layer (AlGaN-based MQW layer, film thickness: 74 nm, Al content of well layer: 0.41), p-type AlGaN layer as p-type cladding layer (Al content: 0.75, film thickness: 20 nm, dopant: Mg) and a p-type GaN contact layer (film thickness: 35 nm, dopant: Mg) are epitaxially grown sequentially.

(Evaluation 2: Measurement of substrate warpage)
After the formation of the intermediate layer and the n-type contact layer on the superlattice laminate, using the optical interference type warpage measuring device (FT-900, manufactured by Niedk) for the group III nitride semiconductor epitaxial substrate of each trial example The amount of warpage of the substrate was measured according to the SEMI standard. The results are shown in Table 1. The “warping amount” in the present invention means a value measured according to SEMI M1-0302. That is, the measurement is performed in a non-forced state, and the amount of warpage is the difference between the maximum value and the minimum value of all measurement point data in the non-adsorption state. As shown in FIG. 11, when the reference plane is a virtual plane obtained by the method of least squares, the warpage (SORI) is represented by the sum of the absolute value of the maximum value A and the minimum value B. The conventionally known group III nitride semiconductor epitaxial substrate has a thickness of about 140 μm. Therefore, a trial example with a warp amount of less than 100 μm was evaluated as “good”, and a trial example with a warp amount of 100 μm or more was evaluated as “x”.

(TEM observation of superlattice laminate)
FIG. 12 shows an enlarged view of the superlattice laminate portion of the TEM image of the cross section of the group III nitride semiconductor epitaxial substrate according to Trial Example 1 (Example 1). The right direction in the drawing is the crystal growth direction, and the portion that appears as a white line in the vertical direction in the drawing is the low Al content layer of the superlattice laminate. In FIG. 12, among the four layers of the low Al content layer of the first laminated body, the first two layers on the substrate side could not be clearly observed, but the first laminated body, the second laminated body, and the third laminated body. It was possible to observe the change in the thickness of each low Al-containing layer. Since the surface of the AlN template, the undoped AlN layer, and the Si-doped AlN buffer layer are the same AlN, dislocation generation occurs at each interface, although the boundary cannot be determined by color in FIG. Since the positions of the sources are aligned, the boundary line can be determined from the dislocation generation position.

  All of the group III nitride semiconductor epitaxial substrates according to trial examples 1 to 3, 5, and 6 (that is, examples 1 to 5) satisfying the conditions of the present invention had both excellent surface flatness and reduced warpage. .

  On the other hand, the group III nitride semiconductor epitaxial substrates according to trial examples 4, 7 to 11 (that is, comparative examples 1 to 6) that do not satisfy at least one of the conditions of the present invention satisfy the conditions of surface flatness and / or warpage. There wasn't.

From these results, the following was found.
Comparing trial examples 1 to 4 in which only the Si-doped impurity concentration is different, when the Si-doped impurity concentration is 1.00 × 10 ¹⁹ / cm ³ or less, it is impossible to achieve both excellent surface flatness and reduced warpage. I understand that.

  Moreover, when trial examples 3 and 7 having the same impurity concentration and different only in the presence or absence of the third laminate are compared, it can be seen that the third laminate is essential in the present invention. Further, comparing trial example 3 and trial example 5 that differ only in the third thickness, the film thickness of the low Al-containing layer of the third laminate is greater than or equal to the film thickness of the low Al-containing layer of the second laminate. I understand that

  Further, comparing trial example 1 and trial example 6, it can be seen that the low Al-containing layer may be either a composition gradient layer or a composition rectangular layer.

  However, as described above, considering the crystallinity when the element formation layer is formed on the group III nitride semiconductor epitaxial substrate, the film thickness (third thickness) of the low Al-containing layer of the third stacked body is as follows. It is considered that it is preferable to be thicker than the film thickness (second thickness) of the two-layered low Al-containing layer. Similarly, considering the occurrence of cracks when the element formation layer is formed, it is considered that the low Al content layer is preferably a composition gradient layer.

  In addition, trial examples 9 and 10 are trial examples in which the number of superlattice laminates is 40.5 (the second laminate and the third laminate are not formed), both of which are the conditions of the present invention. It does not satisfy. However, when both are compared, Trial Example 10 in which the impurity concentration due to Si doping is less than the lower limit of the requirements of the present invention is excellent in surface flatness, while in Trial Example 9 that satisfies the impurity concentration of the present invention requirements, It is inferior in flatness. This difference is considered to be due to the effect of roughening the surface by forming irregularities on the surface of the AlN buffer layer described above due to the influence of Si doping on the AlN buffer layer.

  ADVANTAGE OF THE INVENTION According to this invention, the group III nitride semiconductor epitaxial substrate which enabled the coexistence of the outstanding surface flatness and the reduced curvature, and its manufacturing method can be provided.

10 Group III nitride semiconductor epitaxial substrate 12 Substrate (substrate having at least a surface portion made of AlN)
14 undoped AlN layer 16 AlN buffer layer 20 superlattice laminate 21 first laminate 21A high Al content layer (Al _x Ga _1-x N)
21B low Al-containing layer _{(Al y Ga 1-y N} )
22 second stack 22A high Al-containing layer _{(Al x Ga 1-x N} )
22B low Al-containing layer _{(Al y Ga 1-y N} )
23 third stack 23A high Al-containing layer _{(Al x Ga 1-x N} )
23B low Al-containing layer _{(Al y Ga 1-y N} )
30 Element formation layer 31 Connection layer 32 n-type contact layer 33 n-type cladding layer 34 Multiple quantum well layer (MQW layer)
35 p-type cladding layer 36 p-type contact layer 41 n-side electrode 42 p-side electrode 50 Group III nitride semiconductor light emitting device

Claims (7)

A substrate having at least a surface portion made of AlN;
An undoped AlN layer formed on the substrate;
An AlN buffer layer formed on the undoped AlN layer;
A group III nitride semiconductor epitaxial substrate having a superlattice stack formed on the AlN buffer layer,
The AlN buffer layer is Si-doped with an impurity concentration greater than 1.0 × 10 ¹⁹ / cm ³ ;
The superlattice laminate is formed by laminating a high Al content layer (Al _x Ga _1-x N) having an average composition x in the crystal growth direction of 0.9 <x ≦ 1 on the AlN buffer layer, N sets of low Al-containing layers (Al _y Ga _1-y N) having an average composition y in the growth direction of 0 <y <x and the high Al-containing layers alternately (where n is 4 ≦ n ≦ 10) (It is an integer that satisfies)
The first to (n-2) th low Al-containing layers counted from the AlN buffer layer side have a first thickness, and the (n-1) th low Al-containing layer has the first thickness. A group III nitride semiconductor epitaxial substrate having a second thickness that is greater than a thickness of 1, and wherein the nth low Al-containing layer has a third thickness that is equal to or greater than the second thickness.   2. The group III nitride semiconductor epitaxial substrate according to claim 1, wherein the low Al-containing layer is a composition gradient layer in which an Al composition decreases along a crystal growth direction.   The group III nitride semiconductor epitaxial substrate according to claim 1, wherein the high Al content layer satisfies 0.95 ≦ x ≦ 1.   The group III nitride semiconductor epitaxial substrate according to claim 3, wherein the high Al content layer is an AlN layer (x = 1).   5. The group III nitride semiconductor epitaxial substrate according to claim 1, wherein the third thickness is thicker than the second thickness.   The group III nitride semiconductor epitaxial substrate according to claim 1, wherein the high Al content layer has an equal thickness. Forming an undoped AlN layer on a substrate having at least a surface portion made of AlN;
Forming an AlN buffer layer on the undoped AlN layer;
Forming a superlattice laminate on the AlN buffer layer, and a method for producing a group III nitride semiconductor epitaxial substrate comprising:
In the step of forming the AlN buffer layer, Si is doped so as to have an impurity concentration greater than 1.0 × 10 ¹⁹ / cm ³ ,
In the step of forming the superlattice laminate,
A high Al content layer (Al _x Ga _1-x N) having an average composition x in the crystal growth direction of 0.9 <x ≦ 1 is laminated on the AlN buffer layer, and the average composition y in the crystal growth direction is N sets of low Al content layers (Al _y Ga _1-y N) composed of 0 <y <x and the high Al content layers are alternately laminated (where n is an integer satisfying 4 ≦ n ≦ 10). Hits the,
The thickness of the low Al-containing layer from the first to the (n-2) th counting from the AlN buffer layer side is the first thickness, and the thickness of the (n-1) th low Al-containing layer is A Group III nitride semiconductor epitaxial substrate characterized in that the second thickness is greater than the first thickness, and the thickness of the nth low Al-containing layer is a third thickness equal to or greater than the second thickness. Manufacturing method.